Safe-arm initiator



March 17, 1970 PARKER 3,500,747

SAFE-ARM INITIATOR Filed May 17, 1968 3 Sheets-Sheet 1 FIG. 1 FIG. 2

INVENTOR. LOYD C. PARKER ATTORNEYS March 17, 1970 1.. c. PARKER I 3,

SAFE-ARM INITIATOR Filed May 17, 1968 3 Sheets-Sheet 2 67V s9 59 X e! FIG. 3

1216.5 FIG. 4

INVENTOR. LOYD C. PARKER BY q gc l Walla) ATTORNEYS March 17, 1970 L. c. PARKER SAFE-ARM INITIATOR 3 Sheets-Sheet 3 Filed May 17. 1968 POWER SUPPLY FIG. 6

INVENTOR. LOYD C. PARKER QLWQa 1.1%,

ATTORNEYS 3,500,747 SAFE-ARM INITIATOR Loyd C. Parker, Onley, Va., assiguor to the United States of America as represented by the Administrator of the National Aeronautics and Space Administration Filed May 17, 1968, Ser. No. 730,162 Int. Cl. F42c 13/08 U.S. Cl. 102-702 Claims ABSTRACT OF THE DISCLOSURE A safe-arm firing-type initiator in which a first charge of electrical current is passed to electromagnetic rotor drive coils and electromagnets to cause otation of an out of line ignition bead or primary charge housed within a rotor to a second position in which the primary charge is in line with an explosive output charge and a second electrical current is passed to the ignition bead through internal contacts that close upon alinement and cause suflicient heat to be generated by the bridge wire to thereby ignite the ignition bead and initiator output charge by means of heat, defiagration or detonation, depending upon the type of primary explosive ignition bead employed in a particular initiator.

This invention was made by an employee of the National Aeronautics and Space Administration and may be manufactured and used by or for the Government of the United States without the payment of any royalties thereon or therefor.

This invention relates generally to an electroexplosive initiator and relates in particular to a safe-armed firingtype initiator (SAFTI) wherein all the safety advantages of currently employed electro-mechanical safe-arm fuze systems are incorporated in a standard weight and size initiating unit which has the functioning speed of a relay and construction that enables comprehensive testing to be performed thoroughly, yet inexpensively.

All presently employed electromechanical and mechanical safe-arm devices are designed to house the full-size initiator as an internal component. These devices provide mechanisms which prevent propagation of the explosive or heat and pressure output of the initiator unit to the rest of the explosives system such as the detonators, ig niters, etc. The electromechanical safe-arm device also provides electrical safety to the enclosed initiator by disconnecting its electrical inputs from any outside source and by maintaining a short circuit and internal ground across the initiator bridge wire or heater element until the unit is placed in an armed position.

Prior designs of electromechanical and mechanical safearm devices are normally constructed to withstand the rated output of the enclosed initiator of heat, pressure and shrapnel, while in the safe position without allowing propagation to occur or without exploding and creating hazards to anyone handling or installing the unit. These prior art devices have inherent disadvantages in that in order to withstand the forces generated by the internal initiator, the unit must be large and heavy as compared to the parameters of a single initiator. In addition, the size and weight requirements of the safe-arm prior art devices generally restrict their usage to only those vehicles or explosives systems where space and weight are not too important. Since it is difficult to adapt these units for general use, because of the weight and space limitations, they are not presently used on sounding rocket systems or for providing protection on ancillary explosive systems on both small and large rocket vehicles and the use thereof is almost entirely restricted to destruct systems and to very large military rocket motor systems.

3,500,747v Patented Mar. 17, 1970 In the present invention an attempt is made to provide an electroex losive initiator which, by its internal design features, has all the safety advantages of the presently used electromechanical safe-arm devices but has the weight, size, and features of a standard initiator; the functioning speed of a relay; and construction that enables comprehensive testing to be performed thoroughly, yet inexpensively.

Accordingly, it is an object of the present invention to provide a new and novel safe-arm firing-type initiator.

Another object of the present invention is to provide an initiator having safe-arm features but the weight and size of standard initiators.

Another object of the present invention is a safe-arm firing-type initiator so constructed as to enable comprehensive testing to be performed thoroughly, yet inexpensively.

Another object of the present invention is to provide, in a safe-arm initiator, a rotor which interrupts the explosive energy train at the lowest practical point internal to the imtiator unit.

Another object of the present invention is to provide a relay type action which performs safe-arming or safearmed firing actions in an initiator.

Another object of the present invention is to provide a readily replaceable ignition head or primer mix in an explosive initiator which can be tested and replaced without destruction of the entire initiator heat unit.

According to the present invention, the foregoing and other objects are attained by providing an electroexplosive initiator which, by its internal features, has all the safety advantages of the currently used electromechanical safe-arm fuze devices but has the weight, size and features of a standard initiator. The initiator unit includes a houisng having an explosive train therein and adapted to initiate a missile firing system, or the like, wherein a rotatable rotor disposed in the housing and containing an electrically responsive bridge wire and ignition bead is rotatably movable from a first position in which the ignition bead is diametrically opposed to the remainder of the explosive train to a second position in which the ignition head is in alinement with the explosive train. A magnet is provided at each end of the rotor unit with a pair of electrical coils being provided in the initiator housing which, upon actuation, serve as an electrical magnet and influence rotation of the rotor from its first safe position to its second armed position. The circuit for electrically igniting the initiator head is shorted out and grounded internally when the rotor is in its first safe position and, upon rotation of the rotor to its second position the firing circuit is completed by removing the short and closing internal contacts. Upon application of electrical power to the bridge wire the initiator head is then fired.

A more complete appreciation and many of the attendant advantages thereof will be readily apparent a the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a sectional view of the initiator of the present invention when the rotor is in the safe position;

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1, but with the arming rotor being disposed in the armed position;

FIG. 3 is a sectional view taken along lines 33 of FIG. 2;

FIG. 4 is a partial view of the initiator unit of the present invention when looking along the arrow in FIG. 3;

FIG. 5 is a view of one of the electromagnets with the coil thereof removed; and

FIG. 6 is a schematic diagram of the electrical arming and firing circuit of the present invention.

Referring now to the drawings wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1 there is shown an initiator unit according to the present invention and generally designated by the reference numeral 10. Initiator unit 10 includes a housing 11 having an open threaded end 13 and a connector pin protective sleeve 15 provided at the opposite end. The major length of ignition housing 11 is provided with a longitudinal bore 14 extending from threaded end 13 into the housing unit. A diametrically opposed bore 17 (FIG. 2) is provided through housing 11 and intersects bore 14 adjacent the internal end thereof. Housing 11 is also provided with a counterbore 19 adjacent the end of longitudinally extending bore 14 as will be further explained hereinafter.

As shown more particularly in FIG. 3, a pair of electromagnet pole faces, designated by reference numerals 21 and 23, are disposed in counterbore 19 and each of which is provided with a coil of electrically conductive wire around the electromagnet core thereof as designated respectively by reference numerals 25 and 27. Electromagnets 21 and 23 are retained in position within counterbore 19 by means of a rotor receiving unit 29 which is slidably received Within bore 14 of housing 11. Rotor receiving unit 29 also has four integrally secured electrical leads attached thereto. These two pair of electrical leads are designated respectively as 31 and 33 (FIG. 1), 35 and 37 (FIG. 2). Leads 31 and 33 serve to provide an electrically parallel connection to electric coils 25 and 27, respectively, while leads 35 and 37 serve to provide electrical connection to the ignition charge as will be further explained hereinafter. Rotor receiving unit 29 is also provided with a diametrically opposed bore 39 of essentially the same diameter as bore 17 in housing 11. When placed in the position as shown in FIG. 1 and FIG. 2, rotor receiving unit 29 slidably receives the rotor unit 41. Rotor 41 is provided with a diametrically opposed stepped bore 43 intermediate the length thereof with the smaller step thereof being provided with threads 45 throughout its length. An ignition bead or primer mix 47 is disposed in a suitable threaded cup 49 and threadingly positioned within threaded step 45 of rotor 41. Threaded cup 49 may be composed of any suitable plastic or nonconductive material. A bridge wire i disposed within primer mixed 47 in a conventional manner and connected by way of lead wires 51 and 53 to a pair of electrical contacts 55 and 57 disposed on the exterior circumference of rotor 41. As shown in FIG. 2, when rotor 41 is disposed in the armed condition the electrical contacts 55 and 57 will make electrical connection respectively with the contacts of electrical leads 35 and 37.

As shown more particularly in FIG. 2 and 3, a pair of permanent magnets 59 and 61 are provided integrally secured to opposite ends of rotor 41. The end faces of each magnet 59 and 61 are provided on an are serving to provide a continuous circumferential surface with the rest of rotor unit 41. As shown more particularly in FIG. 5 the ends of the electromagnets are of concave configuration so as to receive the are surface of magnets 59 and 61 therein when rotor 45 is moved to the armed position. Each magnet 59 and 61 is provided with an axle for rotor 41 and as designated by reference numerals 63 and 65. Diametrically opposed bore 17 in housing 11 is closed by suitable end closures 67 and 69, threadingly or otherwise conventionally sealed to housing 11, and serving as bearing structures for axles 63 and 65, respectively. As shown more particularly in FIG. 4, end closure 69 is provided with suitable indicia thereon. A pointer 71, which is conventionally attached to axle 65, serves to point to the indicia on closure 69 to indicate the position of rotor 41 when it is in the safe and armed condition and to manually reposition rotor 41 in safe position when so desired.

ASSEMBLY For assemblying the initiator 10 of the present invention, housing 11 which may be formed by any conventional cast, molding or milling operation and provided with the necessary bores and counterbores therein for receiving the electrical leads 31, 33, 35 and 37, rotor receiving unit 29, electromagnets 21 and 23, and end closures 67 and 69. Electromagnets 21 and 23 are electrically connected to leads 31 and 33 and placed in position within counterbore 19 in housing 11 with rotor receiving unit 29 being slidably received through bore 14 so as to maintain the electromagnets in position. As mentioned hereinbefore, electrical leads 31, 33, 35 and 37 are integrally secured to rotor receiving unit 29 and adapted to be received by suitable insulated bores within housing 11 when the rotor receiving unit 29 is placed in position. Leads 31 and 33 remain internally connected to electromagnets 25 and 27 when the rotor receiving unit 29 is placed in position. Rotor unit 41 with its primer charge having previously been inserted therein is slidably received through diametrically opposed bore 17 in housing 11 and bore 39 within rotor receiving unit 29. Rotor 41 is positioned within housing 11 in the unarmed or safe condition with the electrical contacts 55 and 57 thereon being shorted out against rotor receiving unit 29. End closures 67 and 69 are then placed about axle 63 and 65, respectively, and pointer 71 attached to axle to indicate the rotor is in the safe condition. A suitable propagating charge or explosive train 73 contained, for example, in plastic cup 75 is then slidably positioned within bore 14 of housing 11 so as to be in alinement with primer 47 when the primer charge is ignited. The initiator unit 10 is then in condition to be employed in any suitable initiating system.

OPERATION The operation of the initiating unit 10 of the present invention is now believed apparent but will further be explained in reference to the schematic circuit diagram of FIG. 6. As described hereinbefore electrical leads 31 and 33 are provided in electrical connection with the electrical coils 25 and 27 disposed respectively about the electromagnets 21 and 23 and serve to provide the arming energy to initiator unit 10. When a suitable current is provided through leads 31 and 33, as for example when switch S is closed, electromagnets 21 and 23 are actuated through coils 25 and 27 to influence the rotation of rotor 41 from the safe position shown in FIG. 1 to the armed position shown in FIG. 2 through the influence of the attached magnets 59 and 61. This armed position is indicated by exteriorly disposed pointer 71 provided on axle 65 of rotor 41 and removes rotor contacts 55 and 57 from their ground to a closed position and mated with the contacts formed by electric leads 35 and 37. In the event it is desired not to fire the initiator at this time a reverse polarity current may be applied to leads 31 and 33 cansing rotation of rotor 41 in the reverse position to its safe condition where ignition bead 47 is again shorted. Alternatively, pointer 71 may be manually turned from the armed position indicated in FIG. 4 to that position shown in dotted lines therein to the safe position to provide the initiator 10 again safe with primer charge 47 being shorted out. However, in most instances, once the initiator unit is armed it will be desrable to fire the initiator unit 10 and electrical current will be applied to electrical leads 35 and 37 as, for example, by closing switch S to send current flow through contacts 55 and 57 and leads 51 and 53 to cause heating of the bridge wire within primer 47 to thereby heat or explode the bridge Wire and cause ignition or detonation of primer mix 47 with subsequent ignition or detonation of the main explosive train 73 leading to the system in which firing is desired.

When it is desired to utilize the initiator 10 as a relay type firing system, switch S would be closed first in order that upon actuation of switch S the primer charge 47 would be ignited simultaneously upon being moved to the armed position.

Although the invention has been described in regard to a specific ignition system, it is to be understood that, by the substitution of specific type charges for primer charge 47 and the explosive train 73, the initiator 10 of the present invention may be adapted for the initiator unit in any explosive or ignition type system.

The advantages of the present invention are now believed apparent. Specifically, the present invention provides both electrical and mechanical safety systems inter nal to a normal size electroexplosive initiator or squib which prevent initiation or propagation of the initiator due to any external forces acting' thereon. The electrical arrangement internal to the initiator of the present invention provides complete protection from accidental ignition by electrical, electrostatic or R-F sources. In addition, the internal mechanical safety features of the present invention block the initiator propagation at a point where the explosive energy is normally at its lowest level rather than at some point later in the explosive train where the energy levels become much greater. Also, the relay type action capable of the safe-arm mechanism of the present invention provides an alternate high-speed method of firing this device.

For these applications where it is desirable to provide complete protection, as for example during fiight of a vehicle, the unit would remain in the safe condition with voltage veing supplied the initiator output pins 35 and 37 prior to arming. Firing would then be accomplished by the arming command to the safe-arm initiator through pins 31 and 33. This mode of operation would be especially desirable in manned vehicle systems where an early or unplanned firing would be disastrous. The delay time required for this type of alinement and firing is approximately 30 milliseconds which is comparable with existing firing relays based on measurements made on a specific embodiment of the invention as described herein. This mode of operation, thus, in eflect, combines the initiator, the firing relay and the inter-connecting cable into a single unit thereby greatly improving circuit reliability and safety.

As described hereinbefore, certain features of the present invention provide flexibility in selecting the inputoutput characteristics and for low-cost quality assurance testing. Thus, the initiation charge or primer 47 which is packeged in a bead Within its separate, easily replaceable, threaded cup 49, provides for testing of this charge separately from the main initiator unit to thereby provide a low-cost assurance test of the initiator unit. This low cost item is readily variable with power and resistance requirements suitable to the proposed systems usage. The output charge 73 is also flexible in that both quantity and quality, that is, detonation or defiagration type explosive trains can be carried within the capability of bore 14 within igniter housing 11. Since both the primer and output charge are low-cost, they can be purchased in large quantities for qualification testing and these tests performed in fixtures to verify their reliability. Thus, SAFTI (an acronym for the safe-arm firing-type initiator of the present invention) can be qualified using non-destructive testing techiques applicable to standard relays.

Modifications of the present invention would include, for example, in a purely mechanical system, the rotor could be spring-driven to armed position with a suitable lanyard serving to release the spring pressure to permit the drive of the motor rotor to its armed position. This would involve a simple modification of the end closure bearings to provide a driving spring for rotor 41 with a suitable lanyard release mechanism being disposed on pointer 71 or a suitable extension of axle 65. Also rotor 41 could be spring-loaded to the safe position and be adapted to return to safe position when rotor drive coil voltage is removed giving unit time relay type action. Modification of the end closure bearings and safe arm indicator to provide the spring and removal of the external indicator would readily accomplish this type of modification with the unit being provided with a vacuum seal to prevent out-gassing. In addition to the above, the use of dual bridge wires and dual drive coil design is readily feasible and may be incorporated in the present invention.

There are obviously many other modifications and variations of the present invention readily apparent to those skilled in the art in the light of the above teachings.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A safe-arm firing type explosive initiator comprising:

an initiator housing,

electrical circuitry contained in said housing and in electrical connection with a power supply,

said circuitry including a firing circuit and an actuating circuit,

an explosive train disposed in said housing,

a rotatable rotor in said housing,

said rotor containing an explosive primer and rotatably movable from a first position in which said primer is out of operative alinement with said explosive train to a second position in which said primer is in operative alinement with said explosive train,

means for shorting the electrical connection of said firing circuit and said electrical power means when said rotor is in said first position,

said rotor being rotated by said actuating circuit from said first to said second position and upon reaching said second position said firing circuit serving to ignite said primer to initiate said explosive train,

said housing being provided with (a) a longitudinal cavity extending along the major length thereof and (b) a transverse cavity extending through said housing and intersecting said longitudinal cavity, said explosive train being disposed in said longitudinal cavity and said rotatable rotor being disposed in said transverse cavity,

said rotor consisting of a metallic electrically conductive material, and

said actuating circuit leading electromagnet means disposed about said rotor for influencing rotor rotation.

2. A safe-arm initiator as in claim 1 including:

a pair of end closures for said transverse cavity and adapted to hermetically seal said rotor in said hous- 111g,

one of said closures being provided with indicia therean axle secured to each end of said rotor for rotation therewith and extending through each said closure,

said axle extending through said one closure having a pointer secured thereto and adapted to point to said indicia to indicate the safe and armed position of said rotor.

3. A safe-arm initiator as in claim 2 wherein said pointer also serves as means permitting manual rotation of said rotor from armed to safe position.

4. A safe-arm firing type explosive initiator comprising:

a housing,

an explosive train in said housing,

a rotatable rotor containing an ignition bead for said explosive train and rotatably movable from a first position in which said ignition bead is out of operative alinement with said explosive train to a second position in which said ignition bead is in operative alinement with said explosive train,

electrical firing means for said ignition bead contained within said housing,

means for rendering said electrical firing means inoperative when said rotor is in said first position,

electrical means for influencing rotor rotation from said first position to said second position,

said electrical firing means causing ignition of said ignition bead to ignite said explosive train upon movement of said rotor to said second position, and

said electrical means for influencing rotor rotation including a pair of electromagnets disposed in said housing and a pair of permanent magnets disposed on said rotor.

5. A safe-arm firing type initiator for use as the initiator element in a missile firing system comprising:

an initiator housing,

an explosive train in said housing and adapted to initiate a missile firing system when actuated,

a rotatable rotor in said housing,

said rotor containing an electrically responsive bridge Wire and ignition bead,

said rotor being rotatably movable from a first position in which said ignition bead is diametrically opposed to said exlosive train to a second position in which said ignition bead is in alinement With said explosive train,

means for electrically shorting said electrically responsive bridge wire when said rotor is in said first position to thereby render it safe from electrical actuation,

electromagnet means disposed about said rotor for effecting rotation of said rotor from said first to said second position to simultaneously (1) nullify said means for electrically shorting said bridge Wire and (2) position said bridge wire and ignition bead in operative alinement with said explosive train, and

means for heating said bridge wire and igniting said ignition bead for actuation of said explosive train upon rotation of said rotor from said first to said second position,

said means for heating said bridge Wire being actuated simultaneously with said rotor reaching said second position.

References Cited UNITED STATES PATENTS 2,748,704 6/1956 Dinsmoor 102-70.2

3,052,784 9/1962 Ousley 10270.2 X

3,207,075 9/1965 Semenoff lO2-70.2

3,311,058 3/1967 Fohrrnann et al 10270.2

VERLIN R. PENDEGRASS, Primary Examiner 

